unfortunately, this is a common problem for today's DSLR cameras. unless you only have one do-it-all lens you'll have to deal with this annoying problem. btw, these sensor dust bunnies generally show up in f/stops higher than f/10.
there are two ways to deal with this. one is to actually clean your sensor using a variety of methods such as a hand air blaster (do not ever use compressed air) or by wiping it gently with a swab that has a few drops of chemicals to it. i've actually done this myself with success. it's really not all that hard to do but you must be very careful not to press down too hard on the sensor. once you've overcome your fear then it's pretty easy. it reminds me of how i was too afraid to open up my old 386 to upgrade the memory on it.
the other method is to do it by software. if you have LightRoom go into the Develop module and type N then click on the area to remove the "dust" spot. it's that simple!
i'm sure there are other ways. feel free to share your methods.
